Okay... dropped it on a "testboard" route, found cars that supported the Gilpin Gold Ore product (I had to add it in the session editor), and reread the 'readme' file. It worked for me (TRS2019, build 117009), you do have to back out of the drum (you don't have to uncouple, the script does it) but it worked fine, provided I reasonably centered the car to be unloaded.
One of the best things you can do if you have an issue like this is to make a test route and put in the bare minimum for the asset and try it there using the KISS principle. For instance, with this one, in "create route" I would place the Rotary dump on the map and connect 200-300m of track on either side, and make sure the track on each side was level, then in "create session" I would find a few cars that support the product (that can be a pain) and hook them to my favorite engine [b/c I'm used to it], load the cars, save and run the session with "quick drive" to practice with it.
If you still have issues with it all alone on a route, try deleting and redownloading it, in case of a corrupted file somewhere. As I recall it is a fairly old asset, but it should still work...